The first cut of a newly seeded lawn in the UK is a significant moment that determines the future health and density of the turf. Timing and technique are paramount because the delicate seedlings are still establishing their root structure and are easily damaged. Rushing this process or using an improper method can cause irreversible damage, leading to a thin, patchy lawn instead of the desired verdant carpet. Successfully navigating this initial stage encourages the grass plants to tiller, which is the biological process of lateral shooting that creates a thick, resilient lawn surface.
Assessing Seedling Readiness and Root Stability
The decision of when to cut new grass seed is based on the physical maturity and height of the seedlings, not a calendar date. New grass should reach a height of approximately 7.5 to 10 centimeters (3 to 4 inches) before the first cut. This height ensures the plants have sufficient leaf surface area to generate the energy required for healthy growth and supports tillering—the shift from vertical to horizontal development.
The most reliable way to check readiness is by performing a gentle root stability test. Lightly tug on a few blades of grass; if they pull out easily, the roots are too shallow and the seedlings need more time to anchor themselves. The roots must be developed enough to withstand the force exerted by the mower blades. The soil surface must also be dry enough to support the mower’s weight without causing compaction or rutting, which can displace the young plants.
Premature cutting weakens the seedlings, making them more susceptible to environmental stress and disease.
The Proper Technique for the Initial Mow
The technique used for the inaugural mow is as crucial as the timing and must prioritize minimizing stress on the new plants. Set the mower blades to the highest possible setting, ensuring you remove no more than one-third of the grass blade height. For example, if the grass is 7.5 cm tall, trim off the top 2.5 cm or less.
Sharp blades are necessary, whether using a rotary or a cylinder mower. A dull blade tears the tender grass tips rather than slicing them cleanly, creating wounds that invite disease. A modern rotary mower is often favored for the first cut due to its versatility and ability to handle the longer, uneven growth without snagging the delicate seedlings.
Move the mower slowly and steadily across the new lawn, avoiding sharp turns or abrupt direction changes. Turning sharply can cause the wheels to scuff the surface and rip the shallow-rooted seedlings from the soil. Collect the clippings from this first cut, as leaving them can smother the young plants and encourage thatch formation.
Establishing a Routine and Ongoing Care
Immediately after the initial cut, the lawn requires continued careful attention. If the weather is dry, a light watering is beneficial to help the grass recover, but the ground should never be saturated. This moisture allows the plants to quickly seal the cut ends of the blades and resume photosynthesis.
The cutting height should be lowered very gradually over subsequent mowing sessions. Continue to adhere strictly to the one-third rule for the next few cuts, reducing the height incrementally until you reach your desired final lawn height. This phased approach prevents shocking the grass and allows the plants to adjust their internal energy reserves.
The first application of a general lawn fertilizer should be delayed until the lawn is fully established, typically six to eight weeks after sowing. If a starter fertilizer was not mixed into the soil before seeding, it may be applied once the grass has germinated. Otherwise, wait until the young plants have a robust root system before introducing high-nitrogen feeds.